In reality, Amazon simply changed the way it implements Flash video so that the full range of security technologies are now in force -- including the streaming encryption protocol RTMPE.  (Adobe also offers a DRM technology called Flash Media Rights Management, which controls the use of content once it is on the user's hard drive.)  Amazon didn't use RTMPE before; not only that, but it chose to stream unprotected content to users' hard drives when users played short samples of video content before deciding to purchase it. 

In other words, Amazon opted for weaker security at first, then moved to stronger security once the so-called "hole" was found. (Incidentally, Widevine claims even stronger security for Flash video with its DRM, including the ability to protect against real-time "screen scraping.")

Ars Technica's updated article, together with an Adobe blog entry posted last weekend, paint a truer picture.  Amazon chose to forgo encrypted streaming (and other security measures) because it would decrease network throughput -- always a major concern with Internet streaming video -- and because about 14% of Internet-connected PCs would not be able to play the content. Amazon thus opted to maximize its audience and that audience's experience and assume the risk of content security problems.  What's unclear -- and may never be known publicly -- is whether they did so with the knowledge and cooperation of the movie studios and television networks who license their content to Amazon Video on Demand.